The present invention generally relates to a golf ball, and more particularly, to a golf ball provided with improved dimples.
Conventionally, with respect to the pattern or configuration of dimples on a golf ball, there have been proposed or actually executed many techniques mainly for the purpose of improving flight performance of the golf ball.
Such conventional techniques as referred to above may be broadly divided into one technique which intends to optimize individual shapes of uniform dimples (i.e., diameter, depth, cross sectional shape, etc. of the dimple) as disclosed, for example, in Japanese Laid-Open patent applications Tokkaisho Nos. 60-96272 and 58-25180, etc., and the other technique which defines the interval or pitch between dimples within a predetermined range as disclosed, for example, in Japanese patent Publication Tokkosho No. 58-50744 and Japanese Laid-Open patent Publication Tokkaisho No. 53-115330, and another technique which proposes a mode for arranging all the dimples at an equal pitch as shown in Japanese Laid-Open patent application Tokkaisho No. 57-107170, etc.
What is common to these known techniques is that they are based on the assumption that the individual dimple dimensions are the same for all. Originally, since the golf ball is a spherical body which flies in a golf game at high speeds of 40 to 80 m/sec, and also through rotation at high speeds of 2,000 to 10,000 rpm, it has been conventionally thought that the dimensions concave and convex portions or undulations on the spherical surface of the golf ball affect the force of air flow.
Meanwhile, the role of dimples in a golf ball resides in one point that such dimples reduce the pressure resistance by accelerating the transition of a turbulent flow at the boundary layer to cause a turbulent flow separation, thereby shifting the separating point backwards as compared with laminar flow separation in a golf ball without having any dimples, so as to decrease the separating region for the consequent reduction of pressure resistance, and in the other point that the lift is improved by increasing the difference between the high and low separating points. Moreover, such role must be effectively utilized all through the range from a low speed to a high speed.
However, as shown in FIG. 9, in a prior art golf ball in which dimples "a" having the similar shapes and dimensions are arranged on the peripheral surface of a ball main body, air flows tend to differ from place to place on the surface of the golf ball, and when air flows at cross sections e--e, f--f and g--g intersecting at right angles with a rotary axis b are observed (in FIG. 9 showing the golf ball during flying as seen from above, an arrow H indicates the direction of flight), it is considered that the air flows at the respective cross sections e--e, f--f and g--g interfere with each other, thus undesirably reducing the effect of the dimples. More specifically, during flight in the direction of the arrow H, positions of the separating point E for the cross section e--e, separating point F for the cross section f--f, and separating point G for the cross section g--g, are altered to a large extent (due to the marked difference in the degree of the undulation on the golf ball surface at the respective cross sections), and the air flow at the cross section f--f tends to obstruct the air flows at the cross sections e--e and g--g, thus reducing the dimple effect. On the other hand, it is considered that the air flows respectively at the cross sections e--e, f--f and g--g tend to be stabilized and settled by themselves based on the dimple shape so as to affect the flight of the golf ball from hitting to falling. Therefore, even if it is attempted to optimize the golf ball performance by altering the pattern, pitch, etc. of the conventional similar dimples as shown in FIG. 9, a desired performance can not be sufficiently achieved.